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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. GRB 240502A: Fermi GBM Final Real-time Localization
  2. LIGO/Virgo/KAGRA S240422ed: Host redshifts of AT2024hfq, AT2024hfu, and AT2024hmo from DBSP
  3. Fermi GRB 240501A: Global MASTER-Net observations report
  4. Fermi trigger No 736197684: Global MASTER-Net observations report
  5. GRB 240426A: VZLUSAT-2 detection
  6. GRB 240425A: VZLUSAT-2 detection
  7. MeerKAT Discovery of a Probable Radio Counterpart to EP240414a
  8. GRB240430A: Fermi GBM Final Localization
  9. GRB 240501B: AstroSat CZTI detection
  10. GRB 240501A: Fermi GBM Final Real-time Localization
  11. GRB 240408B: VZLUSAT-2 detection
  12. GRB 240407A: VZLUSAT-2 detection
  13. LIGO/Virgo/KAGRA S240501an: Identification of a GW compact binary merger candidate
  14. X-ray transient EP240414a: Detection of associated supernova
  15. LIGO/Virgo/KAGRA S240430ca: Updated Sky localization and EM Bright Classification
  16. LIGO/Virgo/KAGRA S240430ca: Identification of a GW compact binary merger candidate
  17. LIGO/Virgo/KAGRA S240422ed: GECKO/7DT ToO observations
  18. Additional DECam GW-MMADS Candidates from three nights of observations
  19. GRB 240425A: GRBAlpha detection
  20. Fermi-LAT gamma-ray observations of IceCube-240424A
  21. LIGO/Virgo/KAGRA S240426s: Updated Sky localization
  22. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limit for EP240426a
  23. LIGO/Virgo/KAGRA S240426dl: Updated Sky localization
  24. GRB 240429A: Fermi GBM Final Real-time Localization
  25. LIGO/Virgo/KAGRA S240428dr: Updated Sky localization
  26. LIGO/Virgo/KAGRA S240422ed: GECKO/KMTNet ToO observations
  27. LIGO/Virgo/KAGRA S240429an: Retraction of GW compact binary merger candidate
  28. LIGO/Virgo/KAGRA S240422ed: ENGRAVE VLT/XShooter spectroscopy of the host galaxy of J-GEM24a
  29. LIGO/Virgo/KAGRA S240428dr: Identification of a GW compact binary merger candidate
  30. Fermi GRB 240428A: Global MASTER-Net observations report
  31. GRB 240428A: Fermi GBM Final Real-time Localization
  32. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of J-GEM24a
  33. LIGO/Virgo/KAGRA S240422ed: DDOTI Optical Upper Limit for J-GEM24a
  34. EP240426b: AST3-2 optical upper limit
  35. LIGO/Virgo/KAGRA S240422ed: Observations with 1.6m Mephisto
  36. LIGO/Virgo/KAGRA S240422ed: A transient discovered from Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  37. LIGO/Virgo S240422ed: Swift XRT observation of EP240426a
  38. LIGO/Virgo/KAGRA S240422ed: NOT optical observations of EP240426a
  39. EP240426b: EP-WXT detection of a new fast X-ray transient
  40. LIGO/Virgo/KAGRA S240422ed: Archival radio detection of EP240426a
  41. LIGO/Virgo/KAGRA S240422ed: Swope Follow-up of AT2024hfq, AT2024hfr, AT2024hfs, and AT2024hfx
  42. LIGO/Virgo/KAGRA S240422ed: BOOTES-6/DPRT optical upper limits for EP240426a
  43. LIGO/Virgo/KAGRA S240422ed: GRANDMA Optical Upper Limits for EP240426a
  44. LIGO/VIRGO/KAGRA S240422ed: Historical variability for EP240426a
  45. GRB 240426A: AstroSat CZTI detection
  46. EP240426a: YAHPT optical upper limit
  47. XMM-Newton observation of EP240426a
  48. LIGO/Virgo/KAGRA S240426dl: Identification of a GW compact binary merger candidate
  49. LIGO/Virgo/KAGRA S240422ed: BOOTES-4/MET Optical Upper Limits for EP240426a
  50. LIGO/Virgo/KAGRA S240422ed: EP-FXT Detection of the Potential Opitcal Electromagnetic Counterpart AT 2024hfq Reported by DECam
  51. GRB 240414A: NOEMA detection
  52. LIGO/Virgo/KAGRA S240422ed: EP240426a possible optical detection
  53. LIGO/Virgo/KAGRA S240422ed: Continued Magellan Observations
  54. EP240426a: GMG optical upper limit
  55. LVK S240422ed: Further Swift-XRT followup of three sources
  56. LIGO/Virgo/KAGRA S240422ed: EP-FXT detection of a candidate counterpart EP240426a
  57. LIGO/Virgo/KAGRA S240426s: Identification of a GW compact binary merger candidate
  58. LIGO/Virgo/KAGRA S240422ed: Magellan Follow-up Observations of Swift/XRT candidates
  59. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility contuinued observations of S240422ed and candidate analysis
  60. IceCube-240424A: Upper limits from a search for additional neutrino events in IceCube
  61. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search update and AT2024hfx, AT2024hgl observations
  62. S240422ed: BlackGEM/MeerLICHT transient detection AT2024hgl/MLTJ080628.10-250116.4
  63. LIGO/Virgo/KAGRA S240422ed: PRIME near-infrared observations
  64. LIGO/Virgo/KAGRA S240422ed: 2.5m PRL Telescope follow-up of the Swift/XRT source S240422ed_X190
  65. S240422ed: MeerLICHT/BlackGEM photometry on AT2024hfx and archival ZTF detection
  66. LIGO/Virgo/KAGRA S240422ed: Second night Pan-STARRS observations of the skymap
  67. LIGO/Virgo/KAGRA S240422ed: Further near-infrared observations with Subaru/MOIRCS by J-GEM Collaboration
  68. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-FXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  69. LIGO/Virgo/KAGRA S240422ed: Upper limits from GECAM Observations
  70. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA and Kilonova-Catcher galaxy targeting observations
  71. LIGO/Virgo/KAGRA S240422ed: Additional DECam GW-MMADS Candidates from the first two nights of observations
  72. LIGO/Virgo/KAGRA S240422ed: ANU 2.3m followup of candidate counterparts
  73. LIGO/Virgo/KAGRA S240422ed: Magellan Spectrum of GW-MMADS Candidate AT2024hdo Indicates a Type II SN
  74. GRB 240425A: Fermi GBM Final Real-time Localization
  75. Fermi trigger No 735697285: Global MASTER-Net observations report
  76. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limits for Swift/XRT candidates
  77. GRB 240419B: Swift-BAT refined analysis
  78. GRB 240421B: Swift-BAT refined analysis
  79. GRB 240422A: Glowbug gamma-ray detection
  80. LIGO/Virgo/KAGRA S240422ed: Archival BlackGEM/MeerLICHT detections of AT 2024hdr & AT 2024hdq
  81. LIGO/Virgo/KAGRA S240413p: DESGW DECam Follow-Up
  82. LIGO/Virgo/KAGRA S240422ed: Himalayan Chandra Telescope follow-up of the Swift/XRT source S240422ed_X101
  83. LIGO/Virgo/KAGRA S240422ed: No significant counterpart candidates in HAWC observations
  84. LIGO/Virgo/KAGRA S240422ed: Vetting of DECam Candidates Using Real-Time Resources and SAGUARO Infrastructure
  85. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA/FRAM Observations
  86. IceCube-240424A - IceCube observation of a high-energy neutrino candidate track-like event
  87. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  88. LIGO/Virgo/KAGRA S240422ed: MOSFIRE spectroscopy of the DECam GW-MMADS candidate AT 2024hdn
  89. LIGO/Virgo/KAGRA S240422ed: ATCA follow-up of candidate counterparts
  90. LIGO/Virgo/KAGRA S240422ed: MOSFIRE imaging of the DECam GW-MMADS candidate AT 2024hdm
  91. LIGO/Virgo S240422ed: Swift-XRT detection of 3 possible counterparts
  92. LIGO/Virgo/KAGRA S240422ed: Early X-ray Upper Limits from EP-WXT for the LVK Sky Localization Region
  93. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of Mag24a
  94. LIGO/Virgo/KAGRA S240422ed: Continued Imaging of Mag24a
  95. LIGO/Virgo/KAGRA S240422ed: Archival DECaPSs2 observations of the field of Mag24a
  96. LIGO/Virgo/KAGRA S240422ed: DECam GW-MMADS Candidates
  97. LIGO/Virgo/KAGRA S240422ed: Potential Magellan candidates from GCN 36263 are unrelated.
  98. LIGO/Virgo/KAGRA S240422ed: NOT J-band upper limit on the Swift/XRT source S240422ed_X61
  99. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-WXT for the Three Potential Electromagnetic Counterparts Reported So Far
  100. GRB 240421B: GRBAlpha detection

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