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

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