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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').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. Fermi GRB 250107B: Global MASTER-Net observations report
  2. GRB 250107A: Swift ToO observations
  3. GRB 250107A: Swift/BAT-GUANO arcminute localization of a burst
  4. GRB 250107B: Fermi GBM Final Real-time Localization
  5. GRB 250106A: SVOM/VT 2nd optical deep observation
  6. GRB 250101A: J band upper limit by SYSU 80cm telescope
  7. GRB 250107A: Fermi GBM Final Real-time Localization
  8. EPWXT01709129925: Xinglong optical observations
  9. GRB 250106A: NOT optical observations
  10. LIGO/Virgo/KAGRA S250104v: Updated Sky localization
  11. GRB 250103B: REM optical/NIR upper limits
  12. GRB 250101A: REM optical/NIR counterpart detection
  13. GRB 250106A: Swift-XRT observations
  14. GRB 250106A: SVOM/VT optical candidate
  15. GRB 250106A: Swift ToO observations
  16. The EP-WXT trigger 01709129925 is likely a flaring star
  17. GRB 250106A: SVOM detection of a long burst
  18. Fermi trigger No 757753930: Global MASTER-Net observations report
  19. GRB 241229A: SVOM/VT optical upperlimit
  20. GRB 250103B: Swift-XRT refined Analysis
  21. GRB 250103B: LCO/1m optical afterglow candidate detection
  22. GRB 250103A: Bassano Bresciano Observatory upper limit
  23. GRB 250103B: VLT/X-shooter spectroscopic redshift z = 1.416
  24. GRB 250103A: Swift-XRT observations
  25. GRB 250101A: 1.3m DFOT optical afterglow detection
  26. GRB 241229A: 1.3m DFOT upper limit
  27. GRB 241228B: 1.3m DFOT Optical observations
  28. GRB 241228A: 1.3m DFOT upper limit
  29. GRB 250103A: NOT spectroscopic redshift
  30. GRB 250103B：SVOM/VT optical counterpart
  31. LIGO/Virgo/KAGRA S250104v: Identification of a GW compact binary merger candidate
  32. GRB 250103A: Montarrenti Observatory optical detection
  33. GRB 250101A: further LCOGT optical afterglow observations
  34. GRB 250103A: Redshift 4.01 from OSIRIS+/GTC
  35. GRB 250103A: NOT optical observations
  36. GRB 250103A: TSHAO optical upper limit
  37. GRB 250103A: Fermi GBM Observation
  38. GRB 250103B: LCOGT Optical Upper Limit
  39. IceCube-250102A: Upper limits from a search for additional neutrino events in IceCube
  40. Swift GRB 250103B: Global MASTER-Net observations report
  41. GRB 250103A: SVOM/VT optical counterpart confirmation
  42. EP250101a: Liverpool Telescope optical upper limit
  43. GRB 250103A: Swift ToO observations
  44. IceCube-250101A: Upper limits from a search for additional neutrino events in IceCube
  45. GRB 250101a: Liverpool Telescope optical follow-up
  46. GRB 250103B: SVOM detection of a long burst
  47. GRB 250103B: Swift detection of a burst
  48. GRB 250103A: Xinglong 2.16m Optical Candidate
  49. Fermi GRB 250102A: Global MASTER-Net observations report
  50. GRB 250101B: SVOM/GRM observation
  51. GRB 250103A: GOTO optical upper limit
  52. GRB 250103A: SVOM/C-GFT optical upper limit
  53. GRB 250101A: NUTTelA-TAO / BSTI Optical Limits
  54. IceCube Alert 250102.58: Global MASTER-Net observations report
  55. EP241231b: optical upper limit with the Liverpool Telescope
  56. GRB 250103A: SVOM detection of a long burst (duplicate submission)
  57. GRB 250103A: SVOM detection of a long burst
  58. EP250101a: Xinglong optical upper limit
  59. GRB 250102A: Fermi GBM Final Real-time Localization
  60. LIGO/Virgo/KAGRA S241230bd: Upper limits from Swift/BAT-GUANO
  61. GRB 250101A: Swift-BAT refined analysis
  62. IceCube-250102A - IceCube observation of a high-energy neutrino candidate track-like event
  63. GRB 250101A: further SAO RAS optical observations
  64. GRB 250101A: LCO optical counterpart detection
  65. EP241231b and EP250101a: EP-WXT detection of two X-ray transients
  66. GRB 250101A NUTTelA-TAO / BSTI Early Measurements
  67. GRB 250101A: GMG spectroscopic redshift at z ~ 2.481
  68. GRB 250101A: Swift/UVOT Detection
  69. GRB 250101A: 1.6m Mephisto multi-band optical followup
  70. GRB 250101A: Swift-XRT refined Analysis
  71. Fermi Gamma-ray Burst Monitor trigger 757464861/250101954 is not a GRB
  72. GRB 250101A: Montarrenti Observatory optical observations and rebrightening
  73. IceCube-250101A - IceCube observation of a high-energy neutrino candidate track-like event
  74. GRB 250101A: LCOGT optical afterglow detection
  75. GRB 250101A: OASDG optical observations
  76. Fermi GRB 250101B: Global MASTER-Net observations report
  77. GRB 250101B: Fermi GBM Final Real-time Localization
  78. GRB 250101A: SAO RAS observations of optical brightening
  79. GRB 250101A: BOOTES-4/MET optical afterglow detection
  80. GRB 250101A: AKO Optical Afterglow Detection
  81. GRB 250101A: SAO RAS optical observations
  82. GRB 250101A: Enhanced Swift-XRT position
  83. LIGO/Virgo/KAGRA S250101k: Updated Sky localization and Source Classification
  84. GRB 250101A: Xinglong-2.16m spectroscopic redshift
  85. GRB 250101A: SVOM/C-GFT early optical observations
  86. LIGO/Virgo/KAGRA S250101k: Upper limits from Fermi-GBM Observations
  87. GRB 250101A: MASTER earlier OT observations with SOSS emission features
  88. GRB 250101A: Nanshan/HMT optical observations
  89. GRB 250101A : GIT optical detection
  90. GRB 250101A: GMG Optical Observation
  91. GRB 250101A: Swift detection of a burst with an optical counterpart
  92. Swift GRB250101.56: Global MASTER-Net observations report
  93. GRB 241217a/EP241217b: ATCA Radio Detection
  94. EP241217a: VLA Radio Detection

  95. LIGO/Virgo/KAGRA S241231du: Coverage and upper limit from MAXI/GSC observations
  96. LIGO/Virgo/KAGRA S250101k: Identification of a GW compact binary merger candidate
  97. GRB 241229B: Continued CrAO ZTSh observations
  98. LIGO/Virgo/KAGRA S241231bg: Updated NED Galaxies in the Localization Volume
  99. LIGO/Virgo/KAGRA S241231bg: Updated Sky localization and EM Bright Classification
  100. LIGO/Virgo/KAGRA S241230ev: Updated Sky localization

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