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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 S240422ed: Coverage and upper limits from MAXI/GSC observations
  2. LIGO/Virgo/KAGRA S240422ed: MeerLICHT and BlackGEM observations report
  3. LIGO/Virgo/KAGRA S240422ed: Identification of a GW compact binary merger candidate
  4. LIGO/Virgo/Kagra S240422ed: NED Galaxies in the Localization Volume
  5. LIGO/Virgo/KAGRA S240422ed: Global MASTER-Net observations report
  6. Fermi trigger No 735470374: Global MASTER-Net observations report
  7. GRB 240421A: Glowbug gamma-ray detection
  8. GRB 240414A: radio detection with the VLA
  9. Fermi-LAT gamma-ray observations of IceCube-240419A
  10. GRB 240414A: AMI-LA radio observations
  11. GRB 240414A: LBT optical detection
  12. GRB 240419B : MITSuME Akeno optical upper limits
  13. GRB 240415B: Swift-XRT observations
  14. GRB 240415A: Swift-XRT refined Analysis
  15. Fermi GRB 240422A: Global MASTER-Net observations report
  16. GRB 240421B: AstroSat CZTI detection
  17. GRB 240422A: Fermi GBM Final Real-time Localization
  18. GRB240421B: Zadko Observations
  19. Fermi GRB 240421B: Global MASTER-Net observations report
  20. Swift GRB 240421B: Global MASTER-Net observations report
  21. GRB 240421B: Fermi GBM Observation
  22. GRB 240421B: Swift-XRT refined Analysis
  23. GRB240421B: BOOTES-5/JGT optical upper limit
  24. GRB 240421B: J-band upper limits from WINTER
  25. GRB 240421B: Swift/UVOT Upper Limits
  26. GRB 240421B: Enhanced Swift-XRT position
  27. Fermi GRB 240421A: Global MASTER-Net observations report
  28. EP240417a: no counterpart detection by SOAR
  29. EP240420a: TNT upper limit to its optical counterpart
  30. EP240420a: Xinglong decaying optical counterpart
  31. GRB 240421B: Swift detection of a burst
  32. EP240420a: Nanshan optical counterpart observations
  33. EP240420a: GWAC-F50A optical upper limit
  34. LIGO/Virgo/KAGRA S240421ar: Identification of a GW unmodeled transient candidate
  35. GRB 240421A: Fermi GBM Final Real-time Localization
  36. EP240420a: detection of fading X-ray emission with refined position by EP-FXT
  37. EP240420a: NOT optical counterpart candidate and potential host
  38. Fermi trigger No 735280430: Global MASTER-Net observations report
  39. GRB240419A: Skynet Optical Afterglow Analysis
  40. GRB240418A - Candidate afterglow from NIRES
  41. IceCube Alert 240419.98: Global MASTER-Net observations report
  42. GRB 240419B: Swift/UVOT Upper Limits
  43. IceCube-240419A - IceCube observation of a high-energy neutrino candidate track-like event
  44. IceCube-240419A - IceCube observation of a high-energy neutrino candidate track-like event
  45. EP240420a: EP-WXT detection of a fast X-ray transient
  46. GRB 240419A: Swift/UVOT Upper Limits
  47. GRB 240419B: Swift-XRT refined Analysis
  48. GRB 240419B: optical afterglow from the NOT
  49. LIGO/Virgo/KAGRA S240420aw: Retraction of GW compact binary merger candidate
  50. EP240414a: Near-IR observations with NIRES and WINTER
  51. Swift GRB 240419B: Global MASTER-Net observations report
  52. EP240414A: Terskol Zeiss-2000 optical upper limit
  53. GRB 240419B: Enhanced Swift-XRT position
  54. Swift GRB 240419A: Global MASTER-Net observations report
  55. GRB 240418A: Swift/UVOT Upper Limits
  56. GRB 240419A: REM NIR afterglow detection
  57. GRB 240419A: Swift-XRT refined Analysis
  58. GRB 240418A: Swift-XRT refined Analysis
  59. GRB 240419B: Swift detection of a burst
  60. GRB 240411B: Swift/UVOT Detection
  61. EP240417a: YAHPT Optical Upper Limits
  62. GRB240418A: YAHPT Upper Limits
  63. GRB 240419A: VLT/UVES redshift of z = 5.178
  64. GRB 240419A: VLT optical afterglow detection
  65. GRB 240419A: Enhanced Swift-XRT position
  66. Fermi trigger No 735089036: Global MASTER-Net observations report
  67. EP240416a: J-band observations with WINTER
  68. EP240414a: GMG observation
  69. GRB 240419A: Prompt enhanced Swift-XRT position
  70. GRB 240419A: Swift detection of a burst
  71. GRB 240418A: TSHAO Zeiss-1000 optical upper limit
  72. GRB 240418A: NOT optical upper limits
  73. GRB 240418A: Enhanced Swift-XRT position
  74. GRB 240418A: AKO Upper Limit
  75. GRB 240411A: GOTO early optical upper limits
  76. Swift GRB240418.85: Global MASTER-Net observations report
  77. GRB 240418A: Swift detection of a burst
  78. EP240417a: EP-WXT detection of a fast X-ray transient
  79. Fermi GRB 240417A: Global MASTER-Net observations report
  80. LIGO/Virgo/KAGRA S240413p: X-ray upper limits from EP-WXT for the candidate AGN counterpart
  81. EP240416A: Terskol Zeiss-2000 optical upper limit
  82. EP240416A: Khureltogoot optical upper limit
  83. Improved IPN triangulation of GRB 240411A
  84. EP240416a: BOOTES-2/TELMA Optical Upper Limit
  85. EP240414a: GSP detects optical candidate counterpart AT2024gsa
  86. LIGO/Virgo/KAGRA S240413p: DECam GW-MMADS candidates
  87. IceCube-Cascade 240416A: Upper limits from a search for additional neutrino events in IceCube
  88. GRB 240417A: Fermi GBM Final Real-time Localization
  89. EP240414a: Pan-STARRS detects re-brightening of the candidate counterpart AT2024gsa
  90. LIGO/Virgo/KAGRA S240413p: historical ATLAS and ZTF observations of the candidate AGN counterpart
  91. GRB 240415A: Glowbug gamma-ray detection
  92. GRB 240414A: Glowbug gamma-ray detection
  93. LIGO/Virgo/KAGRA S240413p: STEP - T80S Search and Candidate Counterpart Identification
  94. GRB 240415B: GECAM-B detection
  95. EP 240416a: Xinglong and NOT decaying optical counterpart
  96. GRB 240415A: Swift-BAT refined analysis
  97. EP240416A: MASTER optical observations
  98. GRB 240411A: Glowbug gamma-ray detection
  99. GRB 240414A: Swift-BAT refined analysis
  100. EP240416a: Kinder optical counterpart candidate

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