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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
  1. LIGO/Virgo/KAGRA S240428dr: Updated Sky localization
  2. LIGO/Virgo/KAGRA S240422ed: GECKO/KMTNet ToO observations
  3. LIGO/Virgo/KAGRA S240429an: Retraction of GW compact binary merger candidate
  4. LIGO/Virgo/KAGRA S240422ed: ENGRAVE VLT/XShooter spectroscopy of the host galaxy of J-GEM24a
  5. LIGO/Virgo/KAGRA S240428dr: Identification of a GW compact binary merger candidate
  6. Fermi GRB 240428A: Global MASTER-Net observations report
  7. GRB 240428A: Fermi GBM Final Real-time Localization
  8. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of J-GEM24a
  9. LIGO/Virgo/KAGRA S240422ed: DDOTI Optical Upper Limit for J-GEM24a
  10. EP240426b: AST3-2 optical upper limit
  11. LIGO/Virgo/KAGRA S240422ed: Observations with 1.6m Mephisto
  12. LIGO/Virgo/KAGRA S240422ed: A transient discovered from Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  13. LIGO/Virgo S240422ed: Swift XRT observation of EP240426a
  14. LIGO/Virgo/KAGRA S240422ed: NOT optical observations of EP240426a
  15. EP240426b: EP-WXT detection of a new fast X-ray transient
  16. LIGO/Virgo/KAGRA S240422ed: Archival radio detection of EP240426a
  17. LIGO/Virgo/KAGRA S240422ed: Swope Follow-up of AT2024hfq, AT2024hfr, AT2024hfs, and AT2024hfx
  18. LIGO/Virgo/KAGRA S240422ed: BOOTES-6/DPRT optical upper limits for EP240426a
  19. LIGO/Virgo/KAGRA S240422ed: GRANDMA Optical Upper Limits for EP240426a
  20. LIGO/VIRGO/KAGRA S240422ed: Historical variability for EP240426a
  21. GRB 240426A: AstroSat CZTI detection
  22. EP240426a: YAHPT optical upper limit
  23. XMM-Newton observation of EP240426a
  24. LIGO/Virgo/KAGRA S240426dl: Identification of a GW compact binary merger candidate
  25. LIGO/Virgo/KAGRA S240422ed: BOOTES-4/MET Optical Upper Limits for EP240426a
  26. LIGO/Virgo/KAGRA S240422ed: EP-FXT Detection of the Potential Opitcal Electromagnetic Counterpart AT 2024hfq Reported by DECam
  27. GRB 240414A: NOEMA detection
  28. LIGO/Virgo/KAGRA S240422ed: EP240426a possible optical detection
  29. LIGO/Virgo/KAGRA S240422ed: Continued Magellan Observations
  30. EP240426a: GMG optical upper limit
  31. LVK S240422ed: Further Swift-XRT followup of three sources
  32. LIGO/Virgo/KAGRA S240422ed: EP-FXT detection of a candidate counterpart EP240426a
  33. LIGO/Virgo/KAGRA S240426s: Identification of a GW compact binary merger candidate
  34. LIGO/Virgo/KAGRA S240422ed: Magellan Follow-up Observations of Swift/XRT candidates
  35. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility contuinued observations of S240422ed and candidate analysis
  36. IceCube-240424A: Upper limits from a search for additional neutrino events in IceCube
  37. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search update and AT2024hfx, AT2024hgl observations
  38. S240422ed: BlackGEM/MeerLICHT transient detection AT2024hgl/MLTJ080628.10-250116.4
  39. LIGO/Virgo/KAGRA S240422ed: PRIME near-infrared observations
  40. LIGO/Virgo/KAGRA S240422ed: 2.5m PRL Telescope follow-up of the Swift/XRT source S240422ed_X190
  41. S240422ed: MeerLICHT/BlackGEM photometry on AT2024hfx and archival ZTF detection
  42. LIGO/Virgo/KAGRA S240422ed: Second night Pan-STARRS observations of the skymap
  43. LIGO/Virgo/KAGRA S240422ed: Further near-infrared observations with Subaru/MOIRCS by J-GEM Collaboration
  44. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-FXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  45. LIGO/Virgo/KAGRA S240422ed: Upper limits from GECAM Observations
  46. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA and Kilonova-Catcher galaxy targeting observations
  47. LIGO/Virgo/KAGRA S240422ed: Additional DECam GW-MMADS Candidates from the first two nights of observations
  48. LIGO/Virgo/KAGRA S240422ed: ANU 2.3m followup of candidate counterparts
  49. LIGO/Virgo/KAGRA S240422ed: Magellan Spectrum of GW-MMADS Candidate AT2024hdo Indicates a Type II SN
  50. GRB 240425A: Fermi GBM Final Real-time Localization
  51. Fermi trigger No 735697285: Global MASTER-Net observations report
  52. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limits for Swift/XRT candidates
  53. GRB 240419B: Swift-BAT refined analysis
  54. GRB 240421B: Swift-BAT refined analysis
  55. GRB 240422A: Glowbug gamma-ray detection
  56. LIGO/Virgo/KAGRA S240422ed: Archival BlackGEM/MeerLICHT detections of AT 2024hdr & AT 2024hdq
  57. LIGO/Virgo/KAGRA S240413p: DESGW DECam Follow-Up
  58. LIGO/Virgo/KAGRA S240422ed: Himalayan Chandra Telescope follow-up of the Swift/XRT source S240422ed_X101
  59. LIGO/Virgo/KAGRA S240422ed: No significant counterpart candidates in HAWC observations
  60. LIGO/Virgo/KAGRA S240422ed: Vetting of DECam Candidates Using Real-Time Resources and SAGUARO Infrastructure
  61. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA/FRAM Observations
  62. IceCube-240424A - IceCube observation of a high-energy neutrino candidate track-like event
  63. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  64. LIGO/Virgo/KAGRA S240422ed: MOSFIRE spectroscopy of the DECam GW-MMADS candidate AT 2024hdn
  65. LIGO/Virgo/KAGRA S240422ed: ATCA follow-up of candidate counterparts
  66. LIGO/Virgo/KAGRA S240422ed: MOSFIRE imaging of the DECam GW-MMADS candidate AT 2024hdm
  67. LIGO/Virgo S240422ed: Swift-XRT detection of 3 possible counterparts
  68. LIGO/Virgo/KAGRA S240422ed: Early X-ray Upper Limits from EP-WXT for the LVK Sky Localization Region
  69. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of Mag24a
  70. LIGO/Virgo/KAGRA S240422ed: Continued Imaging of Mag24a
  71. LIGO/Virgo/KAGRA S240422ed: Archival DECaPSs2 observations of the field of Mag24a
  72. LIGO/Virgo/KAGRA S240422ed: DECam GW-MMADS Candidates
  73. LIGO/Virgo/KAGRA S240422ed: Potential Magellan candidates from GCN 36263 are unrelated.
  74. LIGO/Virgo/KAGRA S240422ed: NOT J-band upper limit on the Swift/XRT source S240422ed_X61
  75. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Three Potential Electromagnetic Counterparts Reported So Far
  76. GRB 240421B: GRBAlpha detection
  77. IceCube Alert 240424.08: Global MASTER-Net observations report
  78. LIGO/Virgo/KAGRA S240422ed: Magellan Detection of a Potential Electromagnetic Counterpart
  79. LIGO/Virgo/KAGRA S240422ed: SAGUARO upper limits from CSS
  80. LIGO/Virgo/KAGRA S240422ed: Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  81. LIGO/Virgo/KAGRA S240422ed: LAST optical observations
  82. LIGO/Virgo/KAGRA S240422ed: Potential Candidates from Magellan galaxy-based search
  83. LIGO/Virgo/KAGRA S240422ed: WINTER J-band upper limits on the Swift/XRT source S240422ed_X61
  84. IceCube-240419A: Upper limits from a search for additional neutrino events in IceCube
  85. LIGO/Virgo/KAGRA S240421ar: Updated Sky localization
  86. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam upper limits on the Swift/XRT source S240422ed_X61
  87. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from Pan-STARRS observations of the skymap
  88. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search
  89. LIGO/Virgo/KAGRA S240422ed: No Counterparts in DDOTI/OAN Optical Observations
  90. GRB 240419A: Swift-BAT refined analysis
  91. GRB 240418A: Swift-BAT refined analysis
  92. LXT240402A/GRB240402B: Chandra X-ray detection
  93. LIGO/Virgo/KAGRA S240423br: Retraction of GW compact binary merger candidate
  94. LIGO/Virgo/KAGRA S240422ed: no candidate counterparts from ATLAS observations
  95. GRB 240419A: Possible ATCA radio detection
  96. GRB 240421B: ATCA radio observations
  97. LIGO/Virgo/KAGRA S240422ed: WINTER near-infrared J-band observations
  98. LIGO/Virgo S240422ed: No counterpart candidates in INTEGRAL SPI-ACS prompt observation
  99. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility observations and candidates
  100. LIGO/Virgo/KAGRA S240422ed: GW-MMADS DECam observations

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