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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 240502C: Zeiss-1000 at Koshka observatory observations of GOTO optical counterpart candidates
  2. Fermi trigger No 736461232: Global MASTER-Net observations report
  3. IPN triangulation of GRB 240501B and GRB 240501A - possible episodes of ultra long GRB
  4. Fermi GRB 240504A: Global MASTER-Net observations report
  5. Fermi trigger No 736472503: Global MASTER-Net observations report
  6. GW170817: VLA observations at ~5.5 yrs since merger
  7. GRB 240503A: AstroSat CZTI detection
  8. GRB 240504A: BALROG localization (Fermi Trigger 736492377 / GRB 240504217)
  9. GRB 240504A: Fermi GBM Final Real-time Localization
  10. Fermi trigger No 736387941: Global MASTER-Net observations report
  11. LXT 240402A / GRB 240402B: VLT X-shooter redshift of host
  12. GRB 240502A: GOTO optical upper limit
  13. Fermi trigger No 736379109: Global MASTER-Net observations report
  14. GRB 240502A: Fermi GBM Observation
  15. GRB 240415A 1.3m DFOT Optical upper limit
  16. GRB 240502C: GOTO possible optical counterpart candidates
  17. LIGO/Virgo/KAGRA S240501an: Updated Sky localization and EM Bright Classification
  18. LIGO/Virgo/KAGRA S240430ca: Updated Sky localization and EM Bright Classification
  19. Fermi GRB 240502B: Global MASTER-Net observations report
  20. GRB 240502C: Fermi GBM Final Localization
  21. Fermi GRB 240502A: Global MASTER-Net observations report
  22. GRB 240501B: GRBAlpha detection
  23. GRB 240430A: GRBAlpha detection
  24. GRB 240502B: Fermi GBM Final Real-time Localization
  25. LIGO/Virgo/KAGRA S240422ed: GECKO/KMTNet Transient Candidates
  26. Integral GRB240502.23: Global MASTER-Net observations report
  27. GRB 240502A long GRB detected by INTEGRAL
  28. GRB 240502A: Fermi GBM Final Real-time Localization
  29. LIGO/Virgo/KAGRA S240422ed: Host redshifts of AT2024hfq, AT2024hfu, and AT2024hmo from DBSP
  30. Fermi GRB 240501A: Global MASTER-Net observations report
  31. Fermi trigger No 736197684: Global MASTER-Net observations report
  32. GRB 240426A: VZLUSAT-2 detection
  33. GRB 240425A: VZLUSAT-2 detection
  34. MeerKAT Discovery of a Probable Radio Counterpart to EP240414a
  35. GRB240430A: Fermi GBM Final Localization
  36. GRB 240501B: AstroSat CZTI detection
  37. GRB 240501A: Fermi GBM Final Real-time Localization
  38. GRB 240408B: VZLUSAT-2 detection
  39. GRB 240407A: VZLUSAT-2 detection
  40. LIGO/Virgo/KAGRA S240501an: Identification of a GW compact binary merger candidate
  41. X-ray transient EP240414a: Detection of associated supernova
  42. LIGO/Virgo/KAGRA S240430ca: Updated Sky localization and EM Bright Classification
  43. LIGO/Virgo/KAGRA S240430ca: Identification of a GW compact binary merger candidate
  44. LIGO/Virgo/KAGRA S240422ed: GECKO/7DT ToO observations
  45. Additional DECam GW-MMADS Candidates from three nights of observations
  46. GRB 240425A: GRBAlpha detection
  47. Fermi-LAT gamma-ray observations of IceCube-240424A
  48. LIGO/Virgo/KAGRA S240426s: Updated Sky localization
  49. LIGO/Virgo/KAGRA S240422ed: SRG/eROSITA archival upper limit for EP240426a
  50. LIGO/Virgo/KAGRA S240426dl: Updated Sky localization
  51. GRB 240429A: Fermi GBM Final Real-time Localization
  52. LIGO/Virgo/KAGRA S240428dr: Updated Sky localization
  53. LIGO/Virgo/KAGRA S240422ed: GECKO/KMTNet ToO observations
  54. LIGO/Virgo/KAGRA S240429an: Retraction of GW compact binary merger candidate
  55. LIGO/Virgo/KAGRA S240422ed: ENGRAVE VLT/XShooter spectroscopy of the host galaxy of J-GEM24a
  56. LIGO/Virgo/KAGRA S240428dr: Identification of a GW compact binary merger candidate
  57. Fermi GRB 240428A: Global MASTER-Net observations report
  58. GRB 240428A: Fermi GBM Final Real-time Localization
  59. LIGO/Virgo/KAGRA S240422ed: J-band non-detection of J-GEM24a
  60. LIGO/Virgo/KAGRA S240422ed: DDOTI Optical Upper Limit for J-GEM24a
  61. EP240426b: AST3-2 optical upper limit
  62. LIGO/Virgo/KAGRA S240422ed: Observations with 1.6m Mephisto
  63. LIGO/Virgo/KAGRA S240422ed: A transient discovered from Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
  64. LIGO/Virgo S240422ed: Swift XRT observation of EP240426a
  65. LIGO/Virgo/KAGRA S240422ed: NOT optical observations of EP240426a
  66. EP240426b: EP-WXT detection of a new fast X-ray transient
  67. LIGO/Virgo/KAGRA S240422ed: Archival radio detection of EP240426a
  68. LIGO/Virgo/KAGRA S240422ed: Swope Follow-up of AT2024hfq, AT2024hfr, AT2024hfs, and AT2024hfx
  69. LIGO/Virgo/KAGRA S240422ed: BOOTES-6/DPRT optical upper limits for EP240426a
  70. LIGO/Virgo/KAGRA S240422ed: GRANDMA Optical Upper Limits for EP240426a
  71. LIGO/VIRGO/KAGRA S240422ed: Historical variability for EP240426a
  72. GRB 240426A: AstroSat CZTI detection
  73. EP240426a: YAHPT optical upper limit
  74. XMM-Newton observation of EP240426a
  75. LIGO/Virgo/KAGRA S240426dl: Identification of a GW compact binary merger candidate
  76. LIGO/Virgo/KAGRA S240422ed: BOOTES-4/MET Optical Upper Limits for EP240426a
  77. LIGO/Virgo/KAGRA S240422ed: EP-FXT Detection of the Potential Opitcal Electromagnetic Counterpart AT 2024hfq Reported by DECam
  78. GRB 240414A: NOEMA detection
  79. LIGO/Virgo/KAGRA S240422ed: EP240426a possible optical detection
  80. LIGO/Virgo/KAGRA S240422ed: Continued Magellan Observations
  81. EP240426a: GMG optical upper limit
  82. LVK S240422ed: Further Swift-XRT followup of three sources
  83. LIGO/Virgo/KAGRA S240422ed: EP-FXT detection of a candidate counterpart EP240426a
  84. LIGO/Virgo/KAGRA S240426s: Identification of a GW compact binary merger candidate
  85. LIGO/Virgo/KAGRA S240422ed: Magellan Follow-up Observations of Swift/XRT candidates
  86. LIGO/Virgo/KAGRA S240422ed: Zwicky Transient Facility contuinued observations of S240422ed and candidate analysis
  87. IceCube-240424A: Upper limits from a search for additional neutrino events in IceCube
  88. LIGO/Virgo/KAGRA S240422ed: GOTO counterpart search update and AT2024hfx, AT2024hgl observations
  89. S240422ed: BlackGEM/MeerLICHT transient detection AT2024hgl/MLTJ080628.10-250116.4
  90. LIGO/Virgo/KAGRA S240422ed: PRIME near-infrared observations
  91. LIGO/Virgo/KAGRA S240422ed: 2.5m PRL Telescope follow-up of the Swift/XRT source S240422ed_X190
  92. S240422ed: MeerLICHT/BlackGEM photometry on AT2024hfx and archival ZTF detection
  93. LIGO/Virgo/KAGRA S240422ed: Second night Pan-STARRS observations of the skymap
  94. LIGO/Virgo/KAGRA S240422ed: Further near-infrared observations with Subaru/MOIRCS by J-GEM Collaboration
  95. LIGO/Virgo/KAGRA S240422ed: X-ray Upper Limits from EP-FXT for the Potential Electromagnetic Counterparts Reported by Swift and DECam
  96. LIGO/Virgo/KAGRA S240422ed: Upper limits from GECAM Observations
  97. LIGO/Virgo/KAGRA S240422ed: No significant candidates in GRANDMA and Kilonova-Catcher galaxy targeting observations
  98. LIGO/Virgo/KAGRA S240422ed: Additional DECam GW-MMADS Candidates from the first two nights of observations
  99. LIGO/Virgo/KAGRA S240422ed: ANU 2.3m followup of candidate counterparts
  100. LIGO/Virgo/KAGRA S240422ed: Magellan Spectrum of GW-MMADS Candidate AT2024hdo Indicates a Type II SN

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